MEXICO CITY: Mexican authorities denied Thursday that paramilitaries were operating in the country after the appearance of an armed group that vowed to kill members of the brutal Zetas drug gang.

“There's no indication that this type of phenomenon of paramilitary groups exists,” government security spokeswoman Alejandra Sota told a news conference.

The government this week firmly rejected aid from a group of masked men calling themselves the “Mata Zetas” or “Zeta Killers” who appeared in an online video shortly after 49 bodies were dumped in the eastern city of Veracruz.

The men presented themselves as “the armed wing of the people, for the people,” and highlighted their respect for the Mexican authorities.

Sota said “there are no elements to suggest this group can be called paramilitary.”

Opposition politicians expressed concern that private armies were starting to take on drug gangs amid raging violence, as has been the case with Colombia's drug wars.

“Extrajudicial killings always lead to worse violence,” said leftist senator Pablo Gomez, calling for a report on possible paramilitary activities in Mexico.

Interior Minister Francisco Blake insisted Tuesday that anyone “outside the law who attempts to become a crime fighter... will face the forces of the state.”

The Zetas, set up in the 1990s by ex-elite soldiers turned hired killers, have been fighting their former allies in the Gulf cartel and others in parts of Mexico for more than a year.

Some analysts suggested the new group could be another drug gang fighting a turf war with the Zetas.